Russian President Dmitry Medvedev fired 20 senior prison officials, including the capital's prison chief, following a probe into the death of a jailed lawyer, officials said Friday.

The death of Sergei Magnitsky caused a public uproar last month. Magnitsky was arrested in November 2008 on tax-evasion charges linked to his work with a British investor barred from Russia as an alleged security risk.

Magnitsky's lawyers said he had died after being denied medical assistance at a Moscow jail. Interior Ministry investigators insist that Magnitsky died of heart failure.

Medvedev sacked nearly 20 Federal Penitentiary Service's officials, including the Moscow prisons' chief and the chief of the Butyrskaya jail where Magnitsky spent the last months of his life, according to the text of the presidential decree posted on the Kremlin's Web site.

The Kremlin gave no reason for the move, but Alexander Reimer, director of the Federal Penitentiary Service, told the Ekho Moskvy radio, that the officials were sacked as a result of an ongoing probe into Magnitsky's death.

The service's deputy chief earlier acknowledged violations at the jail where Magnitsky was kept, but did not elaborate what those were.

Magnitsky was involved in defending Hermitage Capital Management and its partner HSBC against an alleged multimillion-dollar fraud and forgery scheme involving Interior Ministry officers. Hermitage CEO William Browder said the scheme involved illegally taking over assets and using them to fraudulently reclaim $230 million in taxes from the state.

Jamison Firestone, Magnitsky's former boss at the law firm Firestone Duncan LLC, said that the president fired the people who were following orders.

"They were not the people who were actively persecuting Sergei and they are not the people who should bear the greatest blame for his illegal arrest and death," he said.

"Sergei was falsely imprisoned by law enforcement officers who he accused of aiding a theft of $230 million from the Russian Treasury," Firestone said.